EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

A new approach for estimating anthropogenic carbon relying on an observational back-calculation method

Marta López-Mozos1, Fiz F. Pérez1, Lidia I. Carracedo2, Geoffrey Gebbie3, and Antón Velo1
Marta López-Mozos et al.
  • 1Instituto de Investigaciones Marinas (IIM-CSIC), 36208, Vigo, Spain (
  • 2Univ Brest, CNRS, Ifremer, IRD, Laboratoire d'Océanographie Physique et Spatiale (LOPS), IUEM, F29280, Plouzané, France.
  • 3Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543.

Around 31% of carbon dioxide derived from human activities (Canth) has been absorbed by the ocean (DeVries, 2014; Gruber et al., 2019; Sabine et al., 2004). This accumulation helps to mitigate atmospheric carbon dioxide (CO2), but in turn leads to severe consequences on marine systems (IGBP, IOC, SCOR, 2013). Both components of CO2, i.e. anthropogenic and natural, present high variability and uncertainties difficult to observe and quantify. In particular, the Canth signal represents a small fraction of the total dissolved inorganic carbon pool (CT) and it is not directly distinguishable from the natural component, resulting in the emergence of back-calculation techniques (Brewer 1978; Chen and Millero, 1979) to derive it indirectly. Over the years, back-calculation techniques have undergone remarkable improvements (Gruber et al., 1996; Sabine et al., 2004; Touratier et al., 2004, 2007; Vázquez-Rodríguez et al., 2009a, 2009b, 2012), resulting in different methods for estimating Canth that, despite providing helpful and advanced results, show various biases and limitations. Here, we present a new approach for estimating Canth that relies on a back-calculation methodology, purely based on carbon data, and provides results that show good agreement with previous global Canth climatologies. Our approach mainly differs from previous methodologies by pioneering using the transport matrix output from a data‐assimilating ocean circulation inverse model (TMI: Total Matrix Intercomparison; Gebbie and Huybers, 2010) to obtain preformed properties, instead of the historical use of Optimum Multiparameter analysis (OMP). This improvement prevents from the need to use (sub)surface-property linear regressions to estimate preformed alkalinity or air-sea CO2 disequilibrium, and allows introducing different corrections for denitrification and, as a novelty, oxygen disequilibrium.

How to cite: López-Mozos, M., Pérez, F. F., Carracedo, L. I., Gebbie, G., and Velo, A.: A new approach for estimating anthropogenic carbon relying on an observational back-calculation method, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15146,, 2023.